1. Field of the Invention
The present invention relates to a process for transmitting a digitized signal according to OFDM (Orthogonal Frequency Division Multiplexing) type multicarrier modulation using N orthogonal channels. The present invention also relates to a transmitter and a receiver for the implementation of this process.
2. Discussion of Background
In the international Patent Application PCT/FR 89/00546 filed in the name of THOMSON-CSF, there is described a particularly high-performance process for transmission using OFDM type multicarrier modulation making it possible to transmit, with a high density, a digitized signal. In the transmission process described, a plurality of orthogonal frequencies is used and an (amplitude/phase) or (real part/imaginary part) pair is transmitted on each frequency, the amplitude/phase or real part/imaginary part pair being one-to-one equivalent to the information to be sent. Moreover, in order to recover at the receiver the information sent according to this process whilst taking into account multiple echoes, various techniques are used such as the associating with the useful transmission interval of a transition interval or guard interval, the use of synchronization signals and especially the use of test-packets which, on reception, enable equalization of the channels to be performed. However, when wishing to use a very large number N of channels, for example 1024 channels, there is in this case a very large spectral occupancy. Indeed, the frequency band used is at least 16 MHz. This poses a number of problems in regard, for example, to the frequency of operation of the signal processing circuits.